Do adenosine A3 receptors exist?

Functional characterization of three adenosine receptor types

“…tissues (see Kennedy et al, 1992a,b for releva: particular the potency of N6-substituted comi GR79236, R-PIA and CPA, was similar to that of NECA. In addition, in this study, we CV1808 and CGS21680 were substantiall' NECA in these tissues, consistent with da binding studies (Bruns et al, 1986; Jarvis et X ever, the results obtained in this study and previous work (Kennedy et al, 1992a) (Collis & Brown, 1983;Cronstein et al, 1988;Haslam & Cusack, 1981;Kusachi et al, 1983). Thus, in dog coronary artery, human neutrophils and human platelets, CV1808 and CGS21680 were similar in potency to NECA, whilst in guinea-pig aorta, both compounds were substantially less active than NECA.…”

“…Thus, variations in the relative potencies of NECA and N6-substituted derivatives such as PIA and CPA led Ribeiro & Sebastiao (1986) to suggest the existence of a sub-type of the adenosine Al-receptor, which they termed A3. However, our own work (Kennedy et al, 1992a) failed to confirm any key differences, leading us to conclude that comparisons of the relative potencies of these agonists provides no evidence to support a sub-classification of adenosine Al-receptors.…”

“…Firstly, to extend our previous observations on the relative potencies of agonists in preparations containing adenosine Al receptors (Kennedy et al, 1992a) to include a wider range of tissues and compounds, and secondly to determine the relative potencies of agonists in a range of preparations usually considered to contain adenosine A2-receptors (guinea-pig aorta, Collis & Brown, 1983;human neutrophil, Cronstein et al, 1988;human platelet, Haslam & Cusack, 1981; dog coronary artery, Kusachi et al, 1983), and so investigate the utility of the A24-/A2b-receptor classification scheme. The compounds used here include a novel adenosine A,-receptor agonist, N-[(1 S, trans)-2-hydroxycyclopentyl]adenosine (GR 79236) and N-[(2-methylphenyl)methyl]adenosine (metrifudil) which was selected since its reported cardiovascular profile in man suggests that it may be a vasodilator (Schaumann & Kutscha, 1972).…”

“…Rat adipocytes were obtained from epididymal fat pads using the methods described by Stratton et al (1985), and the ability of adenosine derivatives to inhibit noradrenalineinduced lipolysis was assessed as described previously (Kennedy et al, 1992a).…”

“…Methods and experimental protocols for the other preparations used have been described in detail previously (Kennedy et al, 1992a). In brief, strips of guinea-pig ileum longitudinal muscle were stimulated electrically at 0.2 Hz (1 ms pulse width; supra-maximal voltage), and the ability of adenosine derivatives to inhibit the electrically-evoked twitch response was measured.…”